This invention is directed to the preparation of polycarbonate polymers or phenolphthalein polycarbonate copolymers and to a method for the recovery of the same in solid form from solutions containing the same.
Polycarbonates are well known in the art and can be prepared according to a variety of processes. Phenolphthalein-polycarbonate copolymers are also known and have been described, for example, in U.S. Pat. No. 3,036,036 and in an article by P. W. Morgan (Journal of Polymer Science: Part A, Vol. 2, page 437 (1964)). Methods for recovering polycarbonates from solutions by non-solvent precipitation are known and are set forth in U.S. Pat. No. 3,267,074. The improved process of the U.S. Pat. No. 3,267,074 reference concerns concurrently contacting in a high speed shearing chamber a polycarbonate solution and a turbulent stream of polycarbonate non-solvent having a Reynolds number of at least 1,500 and being heated above the boiling point of the polycarbonate solvent. The resulting mixture is then passed to a flash drum containing non-solvent maintained at a temperature above the boiling point of the polycarbonate solvent to remove the polycarbonate solvent, leaving a polycarbonate non-solvent slurry, from which the polycarbonate solid can be obtained. However, in such process, it is required that the solids be maintained in the system for a comparatively long residence time and that the non-solvent is heated above the boiling point of the polycarbonate solvent so that ample heat is available at the point of feed injection, thus avoiding the sudden drop of temperature that would otherwise occur on flashing of the polycarbonate solvent. Also, a two-step process of contacting the polymer with non-solvent is required to separate the polycarbonate solvent from the polymer.
Consequently, it is an object of this invention to provide an improved method for recovering polycarbonates in solid form from a solution containing the same.